Mitochondria isolated from livers of animals treated with certain gluconeogenic hormones such as glucagon and the catecholamines have been shown to respire faster in the presence of ADP and phosphate than control mitochondria. In addition, energy-linked functions of these hormone-modified mitochondria are enhanced. The first goal of this proposal is to evaluate the significance of these findings to the overall mechanism of hormone stimulated gluconeogenesis and ureagenesis. The second goal is to learn what component of the membrane changes as a result of hormone treatment and to learn how this change is brought about. In order to evaluate the exact magnitude of the hormone-induced change in respiratory capacity which occurs in the intact cell, maximal respiratory rates will be measured in isolated liver cells by treating the cells with substrate amounts of durohydroquinone and uncoupling agents. Measurements of glutamate and aspartate concentrations in the cells combined with carbon flux determinations suggest that the kinetic parameters of the glutamate-aspartate carrier are altered by gluconeogenic hormones. This phenomenon will be studied in detail at different levels of cellular organization in the presence of substrates and products of the carrier in an attempt to evaluate the basis and significance of the change. Parallel studies will be done with isolated mitochondria. Preliminary experiments suggest that no specific component of the electron transport chain is altered, but that the structural integrity of the mitochondrial membrane may be improved. To investigate this possibility, mitochondrial membrane permeability to H+ and K+ will be measured and the lipids of the membrane extracted and analyzed by radioisotopic chromatographic techniques. Tetracaine will be used as a tool in some of these studies to alter the activity of endogenous mitochondrial phospholipase A which may be a target for hormone action.